Today's mobile phones, laptops, tablet computers, game consoles, set-top boxes, GPS units and other electronics require random access memory. One form of random access memory is dynamic random access memory (DRAM), which is often used because of its high memory density (number of bits stored per unit area or volume).
Examples of background art that describe DRAM devices include U.S. Pat. No. 5,148,399 granted to Cho et al. on Sep. 15, 1992, entitled “Sense Amplifier Circuitry Selectively Separable From Bit Lines For Dynamic Random Access Memory”, and U.S. Pat. No. 7,505,343 granted to Kang on Mar. 17, 2009, entitled “Sense Amplifier Circuit In Semiconductor Memory Device And Driving Method Thereof”.
Cho et al. disclose an integrated circuit memory device that includes a sense amplifier circuit having a first transistor coupling section connected between a pair of bitlines and a pair of sense amplifier nodes. The sense amplifier circuit further includes a first sense amplifier connected between the sense amplifier nodes so as to selectively discharge one of the sense amplifier nodes and a second sense amplifier connected between the sense amplifier nodes so as to selectively charge the other one of the sense amplifier nodes.
Kang discloses a sense amplifier circuit in a semiconductor memory device in which an under-drive is applied to a switching element of a pull-down side of a sense amplifier in order to compensate for poor driving capability in the case of performing a low voltage operation. The sense amplifier circuit includes: a sense amplifier which has a pull-down element composed of an NMOS transistor and a pull-up element composed of a PMOS transistor and is formed between bitlines to perform data exchange; and a drive controller which supplies a drive voltage for the use of pull-up and pull-down operations to the sense amplifier in order to perform the data exchange, and, during a specific time period included in a time for providing the drive voltage, performs an under-drive whereby the drive voltage for the use of the pull-down operation is used so that the sense amplifier is provided with a voltage that is lower than a voltage used in the pull-down operation in a normal state.
One feature of DRAM devices such as those of Cho et al. and Kang is that they must be refreshed in order to retain the data stored therein. Refreshing of the data occurs frequently and consumes power. This can be an issue for battery-operated units such as mobile phones and laptop/tablet computers. Therefore, it would be beneficial to devise power efficient methods and apparatus for refreshing the data stored in a DRAM device.